The present invention relates to a duckbill check valve for use in medical applications, and more particularly, to a miniaturized duckbill flow control valve which operates in forward flow at a low cracking pressure and which provides high volume flow rates.
In a typical administration set arrangement, a Y-site is used to combine two fluid supply lines into a single fluid line leading to an infusion site on a patient. One supply line generally provides a continuous flow of a saline or equivalent fluid and the other supply line is commonly used to provide a prescribed quantity of medication. When the medication is flowing through the Y-site, a check valve provided in the saline line closes in response to fluid pressure exerted by the medication to prevent the medication from flowing into the saline line. A poor check valve seal could permit the medication to enter the saline solution which may result in incomplete delivery of the prescribed quantity of medication.
In addition, check valves for administration sets must also be capable of providing forward fluid flow at very low cracking pressures. This is particularly true when the check valve is provided in the medication supply line. As the medication is administered, the pressure provided by the fluid head continually decreases until a small quantity of the medication is located in the tubing leading to the valve, at which time the pressure head is too low to maintain the valve open, and fluid flow ceases without delivering the entire quantity of medication. Thus, by decreasing the forward flow cracking pressure for the valve, it is possible to ensure that all, or nearly all, of the prescribed medication will be delivered to the patient.
Further, it is important for check valves to introduce as little restriction as possible to the flow of fluid through an administration set. For example, in emergency situations it is desirable for the valve to permit a high flow rate for purging the line of air prior to connecting it to the patient whereby a prescribed medication may be administered without undue delay.
One type of known check valve for use in medical administration sets includes a rubber or elastomeric disk which is located within a rigid housing. The housing typically includes an annular plastic seat for engaging with the disk whereby the disk and seat form a seal preventing back flow through the valve. In order to provide flow through the valve in a forward direction, the elastomeric disk moves in a longitudinal direction out of contact with the seat of the housing whereby fluid may flow around the periphery of the disk as it passes through the valve. Typical disk-type check valves are shown in U.S. Pat. Nos. 3,889,710 to Brost, 4,354,492 to McPhee, and 4,615,693 to Paradis et al.
One limiting characteristic of disk valves results from providing a large sealing area where the rubber disk contacts the hard plastic seat of the housing. As a result of having two dissimilar materials contacting each other across a relatively large area, there is a high probability that leakage will occur due to minute irregularities between the surfaces formed by the elastomeric disk and the plastic housing seat whereby small fissures are formed for permitting fluid leakage during back flow conditions. In addition, disk valves are often subject to variations in performance as a result of changes in the orientation of the valve. For example, in use with a Y-site, the valve may be oriented in an inverted direction and the weight of the disk will be a factor influencing the responsiveness of the valve depending upon the orientation of the valve.
Duckbill valves are another type of valve used in administration sets as a check valve. A duckbill valve is formed of two converging valve lips which meet at a slit wherein the lips are adapted to move apart to open the slit for flow in a forward direction. Usually, the valve is molded unslit and the slit is cut into the valve subsequent to the molding operation such that a pair of complementary mating surfaces are defined on the opposing lips. The valve is preferably formed of a soft elastomeric material such that a positive seal is formed between the lips when the slit is closed to prevent leakage in a back flow direction. In addition, the duckbill valve is adaptable for miniaturization in that the slit provides for a large flow area since the length of the slit when the valve is in the closed position is much less than the circumference of the aperture formed when the slit moves to an open position. Further, because of its inherent stability, the duckbill valve is far less position sensitive than disk valves such that, regardless of the orientation of the valve, the duckbill valve will have consistent performance characteristics.
U.S. Pat. Nos. 4,535,819 to Atkinson et al, 4,535,818 to Duncan et al, 4,566,493 to Edwards et al and 4,612,960 to Edwards et al all disclose duckbill valve structures which are adapted to be used in a medical fluid administration set. In addition, these patents also disclose providing a housing structure wherein the retention of residual air in the area around the valve is minimized by providing a housing structure which extends close to the valve lips whereby problems associated with purging the system of air are minimized. These valves typically require an alignment tab on the valve for cooperating with a slot on the housing whereby the valve is properly aligned with the housing. In addition, these valves are disclosed as being used in conjunction with Y-sites for medical administration sets. However, the size of these valves does not permit them to be directly incorporated into the Y-site, but rather the valve must be enclosed in a housing attached to a branch extending from the Y-site, as shown for example in U.S. Pat. No. 4,535,818.
Accordingly, there is a need for a miniature valve for use in the fluid lines for a medical administration set wherein the valve has a low cracking pressure, accommodates a high fluid flow rate, provides a reliable and positive checking of fluid flow in the reverse flow direction, and which is also relatively insensitive to changes in orientation.